Hand control for a servo system



Jan. 31, 1961 Filed May 12, 1949 mil ill"

D. E. HACKELMAN 2,969,688

HAND CONTROL. FOR A SERVO SYSTEM 5 Sheets-Sheet l v INVENTOR DENVER E.HAGKELMAN BY 'WT'TORNEYS Jan. 31, 1961 E, HACKELMAN 2,969,688

HAND CONTROL FOR A SERVO SYSTEM Filed May 12, 1949 5 Sheets-Sheet 2INVENTOR DENVER E. HAOKELMAN /%M 49%; BY (Q BQ'WRNEYS United StatesPatent HAND CONTROL FOR A SERVO SYSTEM Denver Eldin Hackelman, 1747 N.Cambrian, Bremerton, Wash.

Filed May 12, 1949, Ser. No. 92,935 4 Claims. (Cl. 74-388) (Grantedunder Title 35, US. Code (1952), see. 266) This invention relates to guncontrol devices and more particularly to means for enabling power gundrives to be changed over from automatic control to manual control witha minimum loss of control during changeover.

Power operated drives for guns are generally provided with a controlmeans for automatic operation by a remotely situated gun director andare also ordinarily provided with manual means which may be used tocontrol the gun movement in the event of a failure of the remotecontrol. In the use of such devices there has been experienced a lapseof control during the change-over period from automatic to manualcontrol. This lapse or period when the gun may move in train withoutresponding to the control member may permit undesired and dangerousrotation of the turret with attendant damage to the equipment andpossible danger to life.

In the manual control for gun drives, a differential follow-upconsisting of the usual three elements can be used to control the gunposition. One element of the differential will be moved by hand whileanother component constituting a follow-up element will be driven by thepower gun drive. During the automatic control of the gun drive, the handoperated element of the manual control will be declutched while thefollow-up element will remain connected to the gun drive. Any inertia orfriction remaining on the hand operated element of the manual controlwill cause movement of a third differential element during automaticcontrol. This movement is highly undesirable since the third element ofthe manual control, which is the effective one to cause movement of thegun, will be moved from neutral position. Thus, during change-over tomanual control, an unwanted force will be applied to the gun drive dueto the fact that the third element of the differential has drifted fromneutral position.

It is therefore an object of the present invention to provide a guntraining device and control means therefor which will permit achange-over from remote to local control with a minimum loss of controlduring the change-over.

It is a further object of this invention to prevent any control movementof the manual control means for the gun while the automatic controlmeans is functioning to move the gun in accordance with signals from thegun director. By preventing control movement of the manual control meansduring this time, it is posible to maintain the manual control means inits neutral position so that on change-over to manual control, nomovement of the gun mount will result until the manual control is handactuated.

It is a still further object of this invention to provide means wherebythe hand actuated differential element of manual control will bepositively driven at the same rate as the follow-up differentialelement, so that no control movement of the third differential elementcan result during the time time when the gun drive is automaticallycontrolled.

A still further object of the invention is to provide in power operatedgun drives of the described type, a means to prevent operation of themanual control unless the third control element of the differential issubstantially in neutral position at the time of change-over fromautomatic to manual control.

Other objects and advantages of the invention will hereinafter becomemore fully apparent from the following description of the drawings inwhich:

Fig. 1 is a side elevation of a gun turret employing the presentinvention, portions of the turret being broken Fig. 2 is a schematicview, showing the arrangement of the various mechanical and hydraulicparts; and

Fig. 3 is a detail view of the manual follow-up differential, portionsbeing broken away to further reveal enclosed parts.

Referring to Fig. 1, a gun 1 is mounted in a turret 2 which isjournalled for rotation about its vertical axis on roller path bearings3. The turret is rotated by pinion 4 which co-acts with internal ringgear 6 rigidly secured to a fixed portion 7 of the structure of thevessel in which the gun is mounted. The pinion 4 is supported in gearbox 5 which is fixed to turret 2 and is rotated either by automatic ormanual controls to be later described in order to train the gun. Anelevation screw 8 is provided to elevate and depress the gun and isactuated by power means (not shown) which form no part of the presentinvention.

Referring to Fig. 2, the shaft 9 driven by hydraulic motor 10 carries aworm 11 which drives pinion 4 through gear 12 and shaft 13. Thehydraulic motor 10 is supplied with hydraulic fluid under pressurethrough conduits 14 which are in fluid communication with hydraulic pump15 driven by electric motor 16. The pump 15 and motor 10 form the partsof a conventional Waterbury Gear which is well known in the gun powerdrive art and which has accordingly been illustrated in diagrammaticfashion. A lever arm 17 is connected to the conventional tilting plate(not shown) of the Waterbury Gear in order to control the quantity anddirection of the flow of hydraulic fluid from pump 15 to by.- draulicmotor 10 in order to form a variable speed drive interposed betweenelectric motor 16 and drive pinion 4 as is well known in the art.

It is customary in the art to position the above-mentioned tilting plateby automatic means controlled by a remote gun director in order tocontrol the drive characteristic of the Waterbury Gear. Also provisionis made to operate the tilting plate by means of a handwheel in theevent that the director should fail for any reason.

In the present invention, the automatic control device comprises aconventional synchro or Selsyn motor which is positioned by an electricsignal from a similar synchro generator in the gun director, in suchmanner that angular movement of the synchro generator causes an equalangular movement of the synchro motor as is well known in the art.Rotation of synhcro motor 18 in response to a signal from the gundirector, moves an arm 19 secured to the rotor of synchro motor 18,which in turn moves link 20 and follow-up lever 21. e

A booster cylinder 22 having a piston 23 and piston rod 24 is providedto move the tilting plate arm 17 by means of a link 25 pivoted at itsrespective ends to said piston rod 24 and arm 17. A valve spool 26,slidably moved by an elongated slot conection to follow-up lever 21, isprovided to control the position of booster piston 23 and tilting platearm 17. The stator of synchro motor 18 is rotatably journalled and isrotated in response to movement of the gun turret by means of a geartrain consisting of shafts 29, 32, 35 and 38 and gears 28, 30, 31, 33,34, 36, 37, 39 and 40. l

Displacement of spool valve 26 by rotation of the synchro rotor allowsservo oil under pressure in line 85a to enter cylinder 22 to move piston23 in the opposite direction from the original direction of movement of,valve 26. At this'time, the transfer valve 93 will be positioned tothe'left to allow passage of fluid, as will later be explained. Thepiston 23 will continue to move until the follow-up lever 21, connectedto the piston rod .24, moves va'lve spool 26 to neutral position again.In .the'new position of piston 23 and piston rod 24, the tilting platearm 17is displaced from its central, neutral position and the hydraulicdrive is operative to rotate the turret. As the turret moves intosynchronism with the director, the stator of servo motor 18 will bemoved by the gearing driven by shaft 9 in a direction to move spoolvalve 26 in the opposite direction from its original movement. Thus, thepiston 23 and piston rod 24 will be moved back towards its centralposition, in which, condition tilting plate arm 17 is also in itscentral neutral position and the turret comes to rest.

The turret may be controlled by manual actuation of handwheels 41, 41 ifthe gun director is inoperative or if for any reason it is desired tocontrol the drive locally. Movement of handwheels 41, 41 controls spoolvalve 26a which in turn controls the position of piston 23 and WaterburyGear tilting plate 17 in the same manner as does valve 26 for theautomatic drive. The manual control consists of a difierential controlscrew 42 which is free to move axially and which is moved axially by thecombined action of a nut gear 43 and a screw rotating gear 44. The nutgear 43 is internally threaded to mesh with threads on the exterior ofcontrol screw 42, while screw rotating gear 44 has elongated internalteeth 44:: meshing with a splined shoulder 45 integral with and near oneend of control screw 42. Nut gear 43 and screw rotating gear 44 aresupported for free rotation but are restrained from axial movement bybearings 46, 46 and bearings 47, 47 respectively (Fig. 3). When the nutgear is held from rotation and the control screw 42 is rotated by gear44, the control screw is moved axially. Similarly, when gear 44 is heldagainst rotation, rotation of nut gear 43 will result in axial movementof screw 42. It also follows from the above, that movement of both nutgear 43 and gear 44 at the same speed and in the same direction, willresult in control screw 42 being restrained from any axial movementsince it then rotates at the same speed as the nut gear into which it isthreaded. Screw rotating gear 44 is rotated in response to movement ofthe turret by a drive connected with shaft Handwheels 41, 41 are securedto a shaft 48 which is journalled in a stanchion 49. A gear 50, securedto shaft 48, rotates a shaft 58 by means of an interposed gear trainconsisting of gears 51, 53, 54, 56 and 57 and shafts 52 and 55. A gear59, secured on shaft 60, meshes with nut gear 43. A clutch, indicatedgenerally at 61 having a clutch disc 62 secured to shaft 60 and a clutchdisc 62a splined to shaft 58, is adapted to interrupt the drive fromhandwheels 41, 41 to gears 59 and 43 in its disengaged position. Whenclutch 60 is in its engaged position, rotation of handwheels 41, 41 willresult in an input to the differential screw in the form of rotation ofnut gear 43.

Gear 44 and control screw 42 which is splined thereto, are rotated bythe output shaft 9 of hydraulic motor during rotation of the turret, bymeans of an interposed gear train consisting of gears 39, 40, 63, 64,66, 67 and 69 and shafts 38, 65 and 68.

When control screw 42 is moved axially by diflerential movement of nutgear 43 with respect to gear 44, the spool valve 261: is temporarilymoved by means of a bell crank 70 having an arm 71 urged into engagementwith one end of the control screw 42 by a spring 72. An arm 73 of crank70 is connected by means of a pivotally connected link 74 to a follow-uplever 21a which has an end remote from link 74 pivotally connected topiston rod 24. The connection between control screw 42 and bell cranklever 71 is effected by an integral extension 42a on screw 42 which hasa rounded end adapted to rotate in socket 71a of lever 71.

Displacement of the spool valve 26a by rotation of the handwheels 41, 41causes servo oil to flow from passage 8512 into cylinder 22 to movepiston 23 in the opposite direction from the original direction ofmovement of valve 26a. During this time, transfer valve 93 remains inthe position shown in Fig. 2. Piston 23 will move until the supply ofservo oil is cut oil? by reason of the fact that movement of the pistonrod 24 returns valve 26a to its closed position by means of thefollow-up lever 21a. In the new position of piston 23 and piston rod 24,the tilting plate arm 17 is displaced from its central, neutral positionand the hydraulic drive is operative to rotate the turret.

As the turret rotates, spool valve 26a is moved in the oppositedirection from that originally imparted by the handwheels since gear 44is likewise rotated by shaft 9 while nut gear 43 remains stationary.This movement of gear 44 imparts axial movement to screw 42 which inturn actuates bell lever 70 to return piston 23 to its neutral position.The turret will thus move to a new position and stop when the handwheels41, 41 are moved to a new position, or the turret will move at a uniformvelocity as long as the handwheels are moved at a uniform velocity.

In order to change from local or hand control to automatic control, aselector valve 75 is provided which has a valve spool 76'having a valvestem 77 with a rack gear 78 formed thereon. A pinion 79 is journalledfor rotation in mesh with rack 78 and is adapted to be rotated by ahandle 80 to move selector valve 75 into the desired position. An indexplate 81 is provided to identify the two positions of the valve. Whenthe selector valve is in the position shown in solid lines in Fig. 2,the fluid duct 82 is in fluid communication with a duct 83 whichconnects with-sump 84. In addition, a fluid duct 83a exhausts spoolvalve 26 and 26a to sump 84.

When the handle 80 is moved to the automatic position, duct 82 is placedin fluid communication with duct 85 since spool valve 76 is then in thedotted line position of Fig. 2. Duct 86 is usually filled with liquidunder pressure delivered from sump 84 through ducts 89 and 90 by pump 87driven by motor 88. The valve 91 generally permits communication betweenducts 90 and 86 as will hereinafter be described. With the valve 75 inthe automatic position, duct 82 ports into duct 92 to actuate thetransfer valve 93, and into duct 92a to disengage handwheel clutch 61and to engage a clutch 115 presently to be described.

Clutch '61'is declutched by a shifter lever 61a, pivotally mounted on abracket 61b and having one end thereof operatively engaging clutchmember 62a. Another end of lever 61a engages a piston 61c slidablymovable in a cylindrical recess bored in bracket 6112, the recess beingin fluid communication with duct 92a. When ducts 92a and 82 are ventedto duct 83 and sump 84 by moving selector handle 80 and valve spool 76to hand control position, a spring 61d abutting against clutch disc 62aand a collar 612 on sh'a ft 58 places clutch 61 in its engaged positionto connect handwheels 41, 41 to the differential control mechanism. Whenfluid under pressure is admitted to duct 92a the force of piston 61covercomes spring 61d whereby the clutch elements are disengaged.

The transfer valve 93, shown in 2, has grooves 94 and 95 at the rightend thereof, which in the position shown connect passages 94a, 94b and95a, 95b respectively, to render valve spool 26a operative by the localband control. A spring96 is provided to normally urge valve 93 to theright into its local hand control position. When the selector handle 80is in the automatieposition, pressure fluid passing through ducts 82.and 92 urges transfer valve 93 to the left against the resiliency ofspring 96. In this position grooves 97 and 98 in valve 93 are alignedwith ports 97a, 97b and 98a, 98b respectively, to render valve spool 26and the automatic control operative and to render inoperative the localhand control.

In using the above prior art structure with the selector handle 80 inthe automatic position, the hydraulic motor in rotating the gun, feedsback a response signal to gears 69 and 44 as has been previouslydescribed, and the signal tends to cause differential control screw 42to drift axially in one direction or the other depending on thedirection of motion of the gun, since gears 43 and 59 offer frictionalresistance to rotary motion although they are disconnected fromhandwheels 41, 41

by reason of handwheel clutch 61 being in the disengaging position.

The axial drift of screw 42 causes valve spool 26a to drift away fromits neutral position but this drift will not cause trouble in theautomatic position because ducts 94a and 95a are closed since valve 93will be to the left in Fig. 2. However, when the control selector 80 isshifted to its hand control position, an unexpected and violent movementof the gun will occur due to movement of valve 93 to the right by spring96 when duct 92 is vented after movement of valve 76 by the selector.The drift of the spool valve 26a away from neutral position will allowpressure fluid to immediately enter chamber 22 to actuate the gun drive.This movement persists until response from the hydraulic motor 10rotates gears 69 and 44 to axially move differential control screw 42and valve spool 26a to a point where the latter is in its neutralposition. During this time, motor 10 is required to accelerate the gunat rates far in excess of acceleration rates encountered in normaloperation and the entire drive system may be subjected to damage becauseof this overload.

In order to overcome this difliculty in accordance with the objects ofthe invention, an arrangement is provided which causes gears 43 and 44to rotate at the same speed while the drive is under automatic controlin order to prevent any drift of control screw 42 and valve spool 26afrom their neutral positions. To accomplish this end, a counter-shaft 99is provided which is journalled for rotary movement in bearings 100 and101, about an axis which in the specific modification shown in Fig. 3,is parallel to the axis of control screw 42. Gear 102 is fixed on oneend of counter-shaft 99 by a spline 103 and geared to rotate with gear43 by means of interposed idler gears 104 and 105 which mesh with eachother and with gears 102 and 43 respectively. The idler gears 104 and105 are supported for rotation by pintle 106 and bearing 107 and bypintle 108 and bearing 109 respectively. A gear 110 journalled for freerotation on counter-shaft 99 is geared to gear 44 by means of aninterposed idler gear 111 meshing with gear 110 and gear 69. Idler gear111 is supported for rotation by means of a bearing 112 and a pintle113, which are mounted along with pintles 106 and 108, in a fixedbracket 114.

In order that gear 110 may selectively rotate shaft 99, a clutch isprovided which is generally indicated at 115 and which consists of aclutch plate 116 having friction lining 117 adapted to engage gear 110.Clutch plate 116 is constrained to rotate with shaft 99 by a drivecotter 118 secured at its ends in plate 116 and slidable axially ofshaft 99 in a slot 119 in the shaft. A stub shaft 120 is slidablysupported in a cylindrical recess 122 co-axially bored in counter-shaft99 and is rigidly pinned to clutch plate 116 by cotter 118. Acompression spring 121 located in recess 122 bears against stub shaft120 and the top of recess 122 to normally urge clutch plate 116 awayfrom gear 110 to disengage clutch 115.

In order to engage clutch 115 when required, a Sylphon bellows 123 influid communication with duct 124 and connecting duct 92a is adapted tobe expanded by hydraulic fluid to axially move stub shaft 120: by meansof interposed thrust bearing 125. r The head of the bellows 123 and thelower end of stub shaft 120 both project into the bearing 125 to providefor a rotatable connection. In order to restrain gear 110 againstundesired axial motion, a sleeve 126 is disposed loosely aboutcounter-shaft 99 and abuts gears 102 and 110 at its respective ends.When the selector handle is in the automatic position hydraulic fluidwill pass through ducts 82, 92a and 124 into bellows 123 when valve 91permits, as will be hereinafter described. The fluid in duct 124 willexpand bellows 123 to engage clutch 115 and thus prevent control screw42 from drifting from its neutral position since the clutch 115 willcause gears 43 and 44 to rotate at the same speed duringautomaticcontrol.

In order to prevent operation in either automatic control or handcontrol in the event that the diflerential control screw 42 is displacedfrom its neutral position by more than a predetermined amount, aninterlock valve 91 is provided which is interposed between hydraulicfluid supply duct and duct 86 and which consists of a valve spool 127slidably mounted in a bored valve casing 128. Valve spool 127 isnormally held in the position shown in full lines in Fig. 2 by a cam ofrevolution 129, which is disposed on an extension 130 of control screw42 and which is abreast of the valve spool 127 when the control screw isin its central, neutral position. Since cam 129 is a cam of revolution,it may be rotated without affecting the position of valve spool 127providing cam 129 is not also moved axially. In the above mentioned fulllined position of valve spool 127, with control screw 42 approximatelyin its neutral position, the ducts 90 and 86 are in fluid communicationand hydraulic fluid is ported into duct 86 to selectively actuate thepiston 23 and hydraulic pump 15 by means of valve 26 in automaticcontrol and by means of valve 26a in hand control. In the event thatcontrol screw 42 is moved a predetermined distance axially from itscentral, neutral position, cam 129 will move axially to permit valvespool 127 to be moved to the dotted position shown in Fig. 2 by spring131. In this latter position, delivery of fluid under pressure from duct90 to duct 86 is stopped and duct 86 is vented to a vent duct 132 influid communication with sump 84. Venting of duct 86 and connectingducts 85 and 85a through vent duct 132 precludes movement of transfervalve 93 to the left in Fig. 2 since ducts 82, 92 and 92a are thenvented either through duct vent 83 when the valve 76 is in the handcontrol position or through ducts 85, 86 and vent duct 132 when thevalve 76 is in the automatic control position.

Since duct 86 and connecting duct 85a are vented, both sides and thecenter of hand control spool valve 26a will be vented through eitherduct 83a or ducts 85a, 86 and 132. In the event that piston 23 is dis-'placed from its central position at the time valve 127 is in its dottedline position, valve spool 26a will also be displaced from its centralposition and both ducts 94a and a will be vented, permitting hydraulicfluid in cylinder 22 to flow from one side or the other of piston 23 asthe piston is moved to its central position by one or the other ofrelatively heavy springs 133 or 134. The control lever arm 17 of thehydraulic pump 15 is thus returned to its central inoperative positionand the gun cannot be moved in either automatic or hand control. In theevent that this condition occurs, the control screw 42 and cam 129 maybe returned to their neutral positions by rotating gears 43 and 59 usinghandwheels 41, 41, since clutch 62 will then be engaged due to theaction of spring 61d and duct 92a will be vented under this condition.

With selector handle 80 in the hand control position, valve 76 willnormally vent ducts 92, 92a and 124 respectively, permitting transfervalve93 to be moved by 'a'gseaes's "7 spring 96 to hand controlposition. Also, Tspring61d will u'rge'handwheel clutch 61 to its closedposition and bellows 123 will be collapsed to permit spring 121 todeclutch backgear clutch 115. The handwheels 41, 41 are then operativeto control the drive through clutch 61 andthe differential follow-up 42,43, 44 and valve 26a, without interference from the backgear 102, 104,105, 110 and 111. Upon movement of handwheels 41, 41 the gun hydraulicdrive units 15 and immediately cause the gun to respond by rotating andthe response is fed back into the differential follow-up by the gearinginterposed between gear 39 on hydraulic motor output shaft 9, and gear69 which meshes with'gear 44 of the diiferential follow-up. Thisfollow-up response causes the control screw 42 to remain very close'toits neutral 7 position.

If for any reason control screw 42 should be moved from its neutralposition by an appreciable amount, cam 129 would permit valve 127 to bemoved by spring 131 to a position in which cylinder 22 would be ventedat both sides of piston 23, thus allowing springs 133 and 134 to centerpiston 23 to stop the drive, as previously explained.

In automatic control, valve 76 will normally supply hydraulic fluidunder pressure to ducts 92, 92a and 124 respectively causing transfervalve 93 to move to a position in which valve 26 is operative to controlthe drive in response to movement of synchro motor 18. The fluid in duct92a will cause piston 610 to disengage clutch 61 to eliminate the dragof the handwheel gearing and to make the handwheels inoperative.With'fluid pressure in duct 124, bellows 123will cause clutch 115 toengage to render the backgears 102, 104, 105, 110 and 111 operative tolock gears 43 and 44 for rotationtogether in order to prevent any axialmovement of control screw 42.

If control screw 42 should for any reason move an appreciable amountfrom its neutral position during automatic control or be in such adisplaced position when automatic operation was attempted, cam 129 wouldpermit valve 127 to be moved by spring 131 to a position in which ducts32 and 92 are vented. Spring 96 would then return transfer valve 93 tothe hand control position and the cylinder 22 would then be vented atboth sides of piston 23, allowing springs 133 and 134 to center thepiston 23 to stop the drive as explained above.

Since backgear clutch 115 is operated by bellows 123 supplied withhydraulic fluid through the ducts 90, 86, 85, 82, 92a and 124 under thecontrol of valves 127 and 76, the backgear clutch 115 can only beengaged when the control screw 42 is approximately at its neutralcentral position with the selector valve 76 in its automatic driveposition. The combined effect of the backgearing and the interlock valve91 is to prevent'the differential control screw 42 from drifting fromits neutral position during automatic control so that subsequentshifting to hand control cannot cause any appreciable movement of thegun.

It is to be understood that the form of my invention, herewith shown anddescribed, is to be taken as a preferred example of the same and thatvarious changes in the shape, size and arrangement of parts may beresorted to, without departing from the spirit of my invention. Morespecifically, various other specific means to couple gears 43 and 44together for simultaneousrotation when required, would readily occur toone skilled in the art. The specific booster cylinder, transfer valve,

selector valve and follow-up difierential disclosed herein areillustrative only since their specific aspects form no part of thepresent invention and they may accordingly be replaced by any equivalentelement known to the art without departing from the scope of thisinvention.

The invention herein described maybe manufactured and' used by orfortheGovernment of the UnitedStates 8 of America for governmentalpurposeswithout the'pay ment of any royalties .thereon or therefor.

What is claimed is:

'1. In a gun assembly, the combination'including gun positioning means,manual means and automatic means selectively controlling said gunpositioning meansfsaid manual means comprising a differential unithaving two input members and a differential output member, linkageconnected between the output member and said gunpositioning means actingupon selection of said manual means to control said gun positioningmeans responsive to movement of said output member, a manually movablecontrol element for driving one of said input members, motiontransmitting means driven by said gun positioning means and driving theother of said input members to provide follow-up action, a drive meansinterposed between said two input members including a clutch devicereleasably engageable to connect said one'input member to said otherinput member to prevent differential movement of said output memberduring automatic control of said positioning means when said manuallymovable element is inoperative.

2. The combination defined in claim 1 wherein said manual means and saidautomatic means are hydraulically operated, a fluid supply line for saidmanual means and said automatic means, an interlock valve located insaid fluid supply line, a cam carried at one end of said output member,said cam normally retaining said interlock valve in open position topermit passage of fluid when said output member is in its normal,central position, said interlock valve being movable by said cam toclose said fluid supply line to prevent overload of said gun positioningmeans during manual control or during change-over from automatic tomanual control in the event said output member movesa given amount fromsaid'central position.

3. In a gun assembly having a power driven meansto position the gun,manual control means to selectively actuate said power driven means,said manual control means comprising a first differential unit havingtwo input members and an output'member, one of said input members beingconnected to a manually movable control element and said other inputmember being connected to said power driven means to provide forfollow-up action, said output member being operative to actuate saidmanual control means in response to relative movement of said two inputmembers, automatic control means to selectively actuate said powerdriven means from a remote point, said automatic control meanscomprising a second differential element, selector means movable fromone position to another to render either said automatic control means orsaid manual control means efiective to actuate said power drivenmeans,'a first clutch controlled by said selector means to disconnectsaid one input member from said manually movable element when saidselector is in the automatic control position, a drive means comprisinga second clutch interposed between said two input members, said secondclutch controlled by said selector means and operative when saidselector is in its automatic control position to connect said one inputmember to said other input member so that said two input members rotateat the same speed and no movement of said output member results duringautomatic control.

4. In a selective control system for a power drive,selectable manualcontrol equipment including a differential comprising two inputmembers'and a differential output member, a manually movable controlelement, linkage connected between said output member and said powerdrive and acting upon selection of said manual control equipment tocontrol said power drive responsive to actuation of said output member,a first clutch engageable to connect said manually movable controlelement to one of said input members, means connecting the other'ofsaidinputmembersto said power 'drive'to provide follow-up action, motiontransmitting means interposed between said two input members including asecond clutch acting upon engagement to connect said one input member tosaid other input member to prevent differential movement of said outputmember when said power drive is controlled by means other than saidmanual control unit, and means acting upon selection of said othercontrol means to disengage said first clutch and engage said secondclutch.

References Cited in the file of this patent UNITED STATES PATENTS ErnstJuly 16, 1946 Wright et a1. Nov. 9. 1948

